The present invention relates to electrical contactors and more particularly to electrical contactors in which the current within the contactor's coil or solenoid is controlled in order to reduce contact bounce during activation of the contactor and the wear which results from contact bounce.
In most conventional contactors the full amount of a rectified line voltage is applied to the coil or solenoid when activation of the contactor and closure of the contacts within the contactor is initiated. Consequently, the armature assembly on which the moving contacts are mounted rapidly accelerates and crashes into the stationary magnet which comprises the solenoid. The excess kinetic energy associated with this process results in multiple mechanical rebounds or "contact bounce" which may continue for 10-20 milliseconds or more and involve multiple contact openings and closings during each contactor activation event. Contact bounce leads to high levels of mechanical wear and erosion of the contacts due to repeated arcing.
In the past, some attempts have been made to control the contact closure process in electrical contactors. For example, U.S. Pat. No, 4,833,565 to Bauer et al discloses a system for sensing line voltage conditions and selecting preprogrammed profiles for phase angle modulating full wave format signals applied to the coil of a contactor so as to control the energy employed during the contact closure process. However, these techniques are relatively inflexible in responding to differences between individual contactors and operate in a highly discontinuous fashion with drive voltage being applied to the solenoid during only part of each half wave period of the line voltage signal.
It is therefore an object of the present invention to provide an electrical contactor with the capability of controlling the contact closure process in accordance with electrical conditions and in response to the characteristics of individual contactors.
It is a further object of the present invention to provide a system for automatically controlling the contact closure process in electrical contactors so that contact closure is achieved with a minimum of contact bounce and with reduced mechanical wear and electrical erosion of the contact elements.
It is another object of the present invention to provide a system for controlling contact bounce in electrical contactors which is economical to manufacture, reliable in operation and is of simple design.